I wanted to start a thread specifically about failures within the throttle body concerning the GS300 (1998 in my case)

My symptons were:
VSC, VSC OFF, and ENGINE Lights would come on, followed by my car going into "Limp" Mode, where only that last 25% (if that) of the throttle would respond (basically have to floor the pedal to even move at all).

During the mornings, or when the engine was COLD, the throttle operated normal...then once the car warmed up, usually at about 10 mins, the problem would start...it happened intermitantly at first...1 or 2 days over the course of a week, then it became more consitent, until last week it became a daily problem.

The first part I tried was the Throttle Position sensor, which is on the front side of the throttle body, and the easiest thing to replace...this didnt help at all. $300 part from Lexus, $80 part from RockAuto.com (exacly same part toyota OEM)

THE PART THAT FIXED THE PROBLEM:
===========================================
"THROTTLE CONTROL Motor", which is the long-larger electrical object next to the TPS on a 98 GS300. Problem is solved.
Lexus Part: The Lexus OEM Part NUmber:89672-30020 = $293.54 from Lexus Dealer (Confirmed Arrowhead Lexus of Arizona, Aug 28, 2009)

The Codes I got were P1120 and P1121 - Accelerator Sensor problem. However it wasnt really the Accelerator Sensor, it was the electrical Motor that controls the opening of the Butterfly valve inside the Throttle body.

I found the problem by good old trouble shooting, and using an ohm meter to see if the throttle electric motor was getting voltage, I found that the elec motor just to the left of the TPS was basically freaking out and shutting down. The Accelerator Pedal Sensor is on the Back-side of the throttle body where the throttle cable connects to, and has a spring on it. It was fine.

GS300's are indeed "drive by wire" concerning the throttle...the cable triggers the Accel Pedal Sensor, which sends a signal to the ECU, the ECU then sends power to the Idel Valve Elec Motor (next to the TPS), which opens and closes the mechanical butterfly valve, then thru a set of internal gears, the TPS sensor detects how far the elec motor is actually opening the butterfly valve...its a closed-loop feed-back system, meaning any failure in any sensor will cause the entire systm to fail.

The throttle cable apparently is ONLY there to allow the fail-safe of having that last 10-25% throttle when the electronic system fails...there is a gearbox inside the throtle body which allows the tail end of the throttle to manually engage the butterfly valve...the rest of the time, the butterfly valve is 100% opened and closed via the idle control motor.

This ad is not displayed to registered members.Register your free account today and become a member on Club Lexus!

how about the 400 mines started with the lights on as soon as i start the car and i press tha accelarator and nothing so i cut it off and start it over and the lights still come on but the accel works and it runs and drives normal then after a while the lights go off whats that about?? help fellas

I wanted to start a thread specifically about the Throttle Position sensor, which is on the front side of the throttle body, and
The throttle cable apparently is ONLY there to allow the fail-safe of having that last 10-25% throttle when the electronic system fails...there is a gearbox inside the throtle body which allows the tail end of the throttle to manually engage the butterfly valve...the rest of the time, the butterfly valve is 100% opened and closed via the idle control motor.

Exactly it, turning off the engine resets the motor controller in the TB....and also allows the ECU to re-set that system.

My best guess is that once the ECU detects that the elec motor in the TB is malfunctioning, it cuts power to the thing to prevent something worse happeneing like Wide Open Throttle getting stuck in the ON position..

the fail-safe to get you home is the manual engagement of the throttle cable on the last 10% or so...it will get you up to 55-65 MPH after a while, and causes no damage...because your manually operating the butterfly valve.

Its not 100% guaranteed your problem is the same, however its a good chance.

The Only code my car displayed were P1120 and P1121 - both were Accelerator pedal sensor/motor control related.

If yours is pulling up O2 sensors, or some other code, disconnect the batter for 1 hour, and re-drive the car until the problem happens...then get the codes read from a good ODBII reader...if its accelerator or Throttle body related, then youve narrowed down the problem.

The Throttle cable moves the Accellerator Pedal Sensor, which happens to be located on the back-side of the throttle body. This sensor sends a signal to the ECU Which in turn sends a signal to the Elec motor control on the TB which opens the Butterfly valve, as the butterfly valve opens the gears turn the Throttle Position Sensor which in turn tells the ECU how far the butterfly valve is open.

The throttle cable Only engages Manually the last 10-25% for fail-safe to get you home in the event the electronic system fails.

The Accelerator Pedal sensor COULD be located on the pedal itself, and the throttle cable elminiated, and the car would run just fine...the catch? Well if the electronic sensors fails, you would have NO manual cable to allow you to "Limp" back home...

Perhaps Lexus placed the Accel Pedal sensor on the Throttle Body because it made better sense to keep all the sensors in 1 place, rather than placing 1 sensor in the cabin...maybe on newer models the accell pedal sensor is inside...it doesnt matter.

If you decided to do so, you could take off the Accell pdeal sensor off the TB, and bolt is somewhere else on the car, and you would never know it was bolted somewhere else...however, if one of the sensors failed, since your throttle cable is no longer attached to the TB, you would loose the failsafe limp mode.

where to find "Idle valve motor" for lexus 1998 gs300 and how to change it??

I have exactly the same problem. Where is the best price for "Idle valve motor" for 1998 lexus gs300, is it interchangable with other Toyota models and is there any tips on how to change it??

Quote:

Originally Posted by az-dave

I wanted to start a thread specifically about failures within the throttle body concerning the GS300 (1998 in my case)

My symptons were:
VSC, VSC OFF, and ENGINE Lights would come on, followed by my car going into Limp Mode, where only that last 25% (if that) of the throttle would respond (basically have to floor the pedal to even move at all).

During the mornings, or when the engine was COLD, the throttle operated normal...then once the car warmed up, usually at about 10 mins, the problem would start...it happened intermitantly at first...1 or 2 days over the course of a week, then it became more consitent, until last week it became a daily problem.

The first part I tried was the Throttle Position sensor, which is on the front side of the throttle body, and the easiest thing to replace...this didnt help at all. $300 part from Lexus, $80 part from RockAuto.com (exacly same part toyota OEM)

THE PART THAT FIXED THE PROBLEM:
===========================================
"Idle Valve Motor", which is the larger electrical object next to the TPS on my 98 GS300. Problem is solved.

The Codes I got were P1120 and P1121 - Accelerator Sensor problem. However it wasnt really the Accelerator Sensor, it was indeed to actual electrical Motor that controls the opening of the Butterfly valve inside the Throttle body.

I found the problem by good old trouble shooting, and using an ohm meter to see if the throttle electric motor was getting elev, I found that the elec motor just to the left of the TPS was basically freaking out and shutting down. The Accelerator Pedal Sensor is on the Back-side of the throttle body where the throttle cable connects to, and has a spring on it. It was fine.

GS300's are indeed "drive by wire" concerning the throttle...the cable triggers the Accel Pedal Sensor, which sends a signal to the ECU, the ECU then sends power to the Idel Valve Elec Motor (next to the TPS), which opens and closes the mechanical butterfly valve, then the TPS sensor detects how far the elec motor is actually opening the butterfly valve...its a closed-loop feed-back system, meaning any failure in any sensor will cause the entire systm to fail.

The throttle cable apparently is ONLY there to allow the fail-safe of having that last 10-25% throttle when the electronic system fails...there is a gearbox inside the throtle body which allows the tail end of the throttle to manually engage the butterfly valve...the rest of the time, the butterfly valve is 100% opened and closed via the idle control motor.

I just ordered the Throttle control motor aka idle valve motor for my 98 gs300 from Carson Toyota. I emailed every parts dealer and nobody can beat their pricing. Ask for Gordon, he provided outstanding customer service. I will be installing it later this week. I will follow up with my conclusion on whether it solves my problems w/ the vsc light